1. Field of the Invention
The present invention relates to a heat-generating resistor. More particularly, it relates to a heat-generating resistor for an ink jet head, such as a bubble ink jet head.
2. Description of the Related Arts
Recently, various types of ink jet heads have been developed for projecting ink from a discharging opening and attaching the ink onto a recording medium such as paper, etc. Among them, a bubble ink jet head which discharges ink from an orifice by utilizing heat energy as disclosed in U.S. Pat. No. 4,723,129 and 4,740,796 has advantages such as good response to recording signal and easy formation of multiple projecting openings.
The principal structure of a bubble ink jet head utilizing heat energy as the ink discharging energy is shown in FIG. 1.
In general, a silicon substrate 10 is provided and an insulating layer 12, such as a phosphosilicate glass layer or silicon oxide layer, is formed thereon. A heat-generating resistor 14 located above the insulating layer 12, a protective layer 18 provided on the heat-generating resistor 14, a pair of electrodes 16 positioned below an ink path 20, and an orifice plate 22 are also included.
In this bubble ink jet head, the energy for ink discharge is imparted by the electrothermal transducer having a pair of electrodes 16 and a heat-generating resistor 14 connected electrically to the electrodes 16. That is, when current caused by a pulse voltage is applied on the electrodes 16 to generate heat from the heat-generating resistor 16, the ink in the ink path 20 near the bubble generating region 19 is momentarily heated. When the ink is heated to higher than its boiling point, bubbles of ink are generated at the bubble generating region 19, which cause a discharge pressure due to momentary volume expansion and shrinkage. Finally, drops are projected from an orifice due to the discharge pressure.
During operation, the heat-generating resistor is subjected to a mechanical shock caused by repetitions of the production and extinction of bubbles of ink, and is subjected to a rise or a drop of temperature over 300.degree. C. for a very short period of the time on the order of 1 to 10 microseconds; therefore, the material of the heat-generating resistor must have good durability and stability.
Consequently, various metals, alloys, metallic compounds or cermets beginning with TaN and RuO.sub.2 which are conventionally known as materials of heat generating resistors are not always satisfactory in durability or stability for application to a heat-generating resistor.
Other materials for a heat-generating resistor, such as HfB.sub.2 or TaAl, are patterned with a reactive ion etching method using chlorine-based gas such as Cl.sub.2 or BCl.sub.3, and therefore have the problems of high cost and danger in production.